Composition for the impregnation of cable insulation



Patented Feb. 6, 1934 UNITED STATES PATENT OFFICE COMPOSITION FOR THE IMPREGNATION OF CABLE INSULATION George F. Kennedy, Wilmington, Del., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware No Drawing. Application December 24, 1928 Serial No. 328,318

7 Claims.

My invention relates to an improvement in electrical cable insulation and more particularly to an improved composition including substantially pure and substantially unoxidized abietic acid or its isomers, or such which is only slightly oxidized, and hydrocarbon oil, for use in impregnating paper taping in cable insulation.

As is well known, the manufacture of insulated electric cable of a certain type includes wiredrawing, stranding, taping with paper, cabling,

-'iS increased the temperature at which the impregnating compound sets is higher. The rosin, when used, has been ordinary commercial rosin containing about 92% of abietic acid or its isomers, oxidized and unoxidized, and about 8% of 5- resenes, or unsaponifiable matter consisting mainly of high boiling essential oils and rosin oil, and in certain cases a small proportion of unsaponifiable solids.

When hydrocarbon oils are used alone for impregnating the paper taping, such are disadvantageous since the oils become oxidized and though they may have initially low dielectric loss, this dielectric loss will increase considerably as the oils are oxidized. When cables are im- 5' pregnated with hydrocarbon oils compounded with either wood or gum rosin this objection is partially overcome. The dielectric loss remains fairly constant throughout the life of the cable although initially the dielectric loss of the com- 4'ofpound of rosin and hydrocarbon -oils may be greater than hydrocarbon oils alone.

Now in accordance with my invention, I have discovered that if substantially pure abietic acid, alone or admixed with its isomers, i. e. abietic acid 46" substantially free from resenes, and substantially unoxidized, be compounded with hydrocarbon oils, the disadvantages of hydrocarbon oils with or without the addition of rosin will be avoided, since the abietic acid will act as an anti-oxidant to resoitard the oxidation of the hydrocarbon oils which oxidation of hydrocarbon oils, if allowed to proceed, would result in greater dielectric loss.

I have also discovered that substantially unoxidized abietic acid or its isomers have a lower 65' viscosity than oxidized abietic acid and that this is true of impregnating compounds in which abietic acid is incorporated. For this reason substantially pure and substantially unoxidized abietic acid can be used in greater proportion in impregnating compounds and still maintain a desired set point.

I have discovered that impregnating compounds made from substantially pure and substantially unoxidized abietic acid and hydrocarbon oils do not sludge. Impregnating compounds made from commercial wood or gum rosins do sludge. The sludging of impregnating compounds is objectionable.

The electrical measurements of a substantially pure and substantially unoxidized abietic acid are as follows:

Temperature in degrees centigrade Resistivity megohms centimeters x 10 Power factor percent Dielectric strength kilovolts inductive capacity The dielectric strength measurements are made with inch sphere electrodes using a mil.

gap.

The substantially pure and substantially unoxidized abietic acid may be obtained in any known manner, and for example, may be obtained by fractional distillation of rosin under vacuum. It is, however, preferably obtained by selective solvent separation of substantially unoxidized rosin from commercial rosin and subsequent fractional distillation of this substantially unoxidized rosin under vacuum, to avoid decomposition.

The substantially pure abietic acid may be used with a hydrocarbon oil in amounts from 5 to 50% It will be understood that in accordance with my invention the substantially pure abietic acid may be compounded with any hydrocarbon oil heretofore used for impregnating cable insulation, as cylinder oil, petrolatum, etc. and it will be understood that I intend the isomers of abietic acid or mixtures of abietic acid and its isomers substantially free from resenes, and slightly oxidized abietic acid as equivalents of substantially pure abietic acid.

What I claim and desire to protect by Letters Patent is:

5. A cable insulation comprising in combination a fibrous material impregnated with a hydrocarbon oil and rosin substantially free from oxidized components.

6. A composition for the impregnation 01' cable insulation which contains a high boiling hydrocarbon oil and rosin substantially free from oxidized components.

'7. In combination a fibrous material impregnated with a high boiling hydrocarbon oil and rosin substantially free from oxidized components.

GEORGE F. KENNEDY. 

